Generally, in a belt transmission device for driving engine accessories such as an alternator, a compressor for an air conditioner, and a water pump, a hydraulic auto-tensioner is coupled to a pivotable pulley arm supporting a tension pulley, the pulley arm is biased by adjusting force applied to the pulley arm from the hydraulic auto-tensioner such that the tension pulley is pressed against a belt, and the tension change of the belt is absorbed by the hydraulic auto-tensioner, thereby keeping the tension of the belt constant.
Since such a belt transmission device is attached to the exterior of an engine, foreign objects such as dust or muddy water might go into a fulcrum bearing portion about which the pulley arm pivots. If such foreign objects go into the fulcrum bearing portion, it resists the pivoting motion of the pulley arm or it extremely shortens the service life of the bearing portion. Therefore, it is necessary to take a countermeasure in the fulcrum bearing portion so as to prevent foreign objects from going into the fulcrum bearing portion.
The below-identified patent document 1 discloses a fulcrum bearing device for a pulley arm in which a countermeasure is taken so as to prevent foreign objects from going into the bearing device.
In the fulcrum bearing device for a pulley arm disclosed in U.S. Pat. No. 7,901,140, a sleeve configured to function as a fulcrum shaft is inserted in a shaft hole of a tubular boss portion connected to the pulley arm, sliding bearings are incorporated between the shaft hole and the outer diameter surface of the sleeve so as to support the sleeve and the pulley arm such that the sleeve and the pulley arm are rotatable relative to each other, washers are fitted on small diameter tube portions formed at the respective end portions of the sleeve, a bolt inserted through the sleeve is screwed into an engine block and tightened, and the sleeve and the washers are fixed in position by means of the bolt, thereby supporting the pulley arm such that the pulley arm is pivotable about the sleeve.
As illustrated in FIG. 15(a), an annular recess 62 having a diameter larger than the diameter of a shaft hole 61 is formed at each end of the shaft hole 61 of a boss portion 60, each seal member 63 is incorporated in the corresponding recess 62, an annular base portion 63a of the seal member 63 is fitted on each end portion of a sleeve 64, a pair of seal lips 63b, 63c extending obliquely away from each other are integrally connected with each of the base portions 63a, the distal end portion of each of the seal lips 63b is in kept in elastic contact with the side surface of the corresponding recess 62, and the distal end portion of each of the seal lips 63c is kept in elastic contact with the inner side surface of a washer 65. Therefore, the seal members 63 prevent foreign objects such as dust or muddy water from going into the shaft hole 61 of the boss portion 60 in which sliding bearings 66 and the sleeve 64 are incorporated.